1. Field of the Invention
The present invention relates to cyclic silylureas and their preparation, to their cyclosilazane starting materials and their preparation, and to aminoalkylalkoxysilanes used to make cyclosilazanes and their preparation. More particularly, the present invention relates to cyclic silylureas which retain the cyclosilazane ring structure after formation. Cyclic silylureas of the present invention are used as additives in formulations for room temperature vulcanizing (RTV) coatings, adhesives and sealants to impart fast cure and reduced volatile organic compound (VOC) release, such as the release of methanol.
2. Prior Art
There has been a continuing need in the adhesives and sealant industry for faster-curing silicone systems, allowing more rapid assembly of full-strength articles of manufacture, including automobiles. There has been a more recent need to have such systems cure with lower, more environmentally acceptable levels of volatile organic compounds.
Fast curing can be attained with systems based on a polyfunctional silazane (i.e., compounds with Si--N bonds) as curing agents. Such systems typically cure by releasing low molecular weight organic amines or ammonia, which are environmentally undesirable because of unacceptable odor and toxicity. Cyclosilazanes and derivatives are compounds with Si--N bonds which cure at high rates by cleaving the Si--N bond without release of volatile organic compounds.
Cyclosilazanes have not achieved commercial acceptance in the industry because of the inability to produce them easily and in large quantity. Earlier attempts at making even small quantities have suffered from a combination of low efficiency and high cost, coupled in some cases with generation of high levels of hazardous waste by-products which require costly disposal by incineration or land-filling.
Thus, there is a need for cyclosilazane-based curing agents for silicone and related adhesive systems which can be prepared in commercial equipment with high efficiency at practical cost of production and waste disposal, and which provide high curing rates with reduced generation of volatile organic compounds. Surprisingly, that need is met by the cyclic silylureas and cyclosilazanes of the present invention.